Japanese unexamined patent application publication No. JP-A-H07-225544 (Patent Document 1) describes a related art image forming apparatus. In the related art image forming apparatus for an electro-photography system, there is an image forming apparatus in which a tandem system is adopted. In the tandem type image forming apparatus, a plurality of photosensitive bodies corresponding to respective colors are arranged along a moving direction of a recording medium. When forming an image, an electrostatic latent image is formed on a photosensitive body, which is driven and rotated, by exposing the photosensitive body to light by exposing means and a visible image is obtained by developing the corresponding electrostatic latent image, onto the recording medium. The above described operations are carried out in the order from an upstream side photosensitive body, thereby forming a color image (that is, a combined image).
Herein, if the rotating speed of the respective photosensitive bodies is constant at all times, it is possible to form a color image, in which line spacing of the respective color images is even, on the recording medium, by executing exposure of respective lines based on image data at a fixed time interval one after another. However, since the rotating speed of the photosensitive body actually fluctuates cyclically, an abnormal color image in which line spacing of respective color images is uneven sometimes maybe formed, and the image quality is adversely influenced.
Therefore, in the related art image forming apparatus, there is an image forming apparatus that is configured to prevent unevenness in line spacing resulting from fluctuations of the rotating speed of photosensitive bodies (Refer to Patent Document 1).